Forces all children to get equal horizontal space. The natural size width will be based on the largest child. Default: "NO". Notice that this does not changes the children size, only the available space for each one of them to expand. (since 3.0)

Defines a margin in pixels, CMARGIN is in the same units of the SIZE attribute. Its value has the format "widthxheight", where width and height are integer values corresponding to the horizontal and vertical margins, respectively. Default: "0x0" (no margin). (CMARGIN since iup-3.0)

Normalizes all children natural size to be the biggest natural size among them. All natural width will be set to the biggest width, and all natural height will be set to the biggest height according to is value. Can be NO, HORIZONTAL, VERTICAL or BOTH. Default: "NO".

The box can be created with no elements and be dynamic filled using Append or Insert.

The box will NOT expand its children, it will allow its children to expand according to the space left in the box parent. So for the expansion to occur, the children must be expandable with EXPAND!=NO, and there must be room in the box parent.